Being well-prepared for battle engenders success; when the foe is cancer, early detection results in a greater likelihood that medical intervention will be successful. At early stages, treatments can often be targeted only to the affected tissues, diminishing side effects. If not caught early, cancer cells may metastasize and spread throughout the body. The prognosis in this case is more dire, and medical treatments are often applied systemically, killing not only cancer cells, but large numbers of healthy cells.
A hallmark of a cancer cell is uncontrolled proliferation. Cancer cells may also exhibit morphological and functional aberrations. Cancer cells may display less organized cellular morphology; for example, losing the asymmetric organelle and structural organization (cell polarity) that allows for proper cell function. Cell-cell and cell-substratum contacts, the specificities of which are also necessary for normal function, are often modulated or lost. Functionally, the cells may carry on few, if any, wild-type functions, or may have exaggerated, unregulated normal functions, such as hormone secretion. Such cells regress to early developmental stages, appearing less differentiated than their wild-type (i.e., normal) parents.
Cancer cells also often mis-express or mis-target proteins to inappropriate cellular compartments. Proteins may be up- or down-regulated; even proteins not usually expressed by a specific cell type can be expressed by the transformed counterpart. Protein mis-expression can have a plethora of downstream cellular effects, including drastic changes in membrane composition, organelle formation, or physiology. Mis-targeting of proteins (and other molecules, such as lipids, etc.) also contributes to the loss of cell polarity.
Detecting cancer growths are complicated by a variety of factors, including protein mis-expression and cellular dedifferentiation. For example, cancers can proceed gradually, being present in only small numbers that are difficult to detect. A common diagnostic approach is the use of certain proteins as “markers” to distinguish cancer cells from healthy ones. For example, prostate cancer diagnoses often use prostate-specific antigen (PSA). These assays require that a marker be defined, have detection agents, and be readily available. However, a marker that is present in a many, if not most, cancers has yet to be defined. Such a marker would remarkably facilitate diagnosis.